This invention generally relates to manufacture of materials and devices. More particularly, the present invention provides a method and device using wafer-bonded crystals or the like in combination with optical devices composed of a gallium-containing nitride crystal. More specifically, embodiments of the invention include techniques for fabricating a light emitting diode device using bulk gallium nitride containing materials, for example for application to optoelectronic devices. In other embodiments, the invention provides a method of manufacture using an epitaxial gallium containing crystal with a release layer. Such crystals and materials include GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others, for manufacture of bulk or patterned substrates.
Progress has been made during the past decade and a half in the performance of gallium nitride (GaN) based light emitting diodes (LEDs). Devices with a luminous efficiency higher than 100 lumens per watt have been demonstrated in the laboratory, and commercial devices have an efficiency that is already superior to that of incandescent lamps, and competitive with that of fluorescent lamps. Further improvements in efficiency are desired to reduce operating costs, reduce electricity consumption, and decrease emissions of carbon dioxide and other greenhouse gases produced in generating the energy used for lighting applications.
Silicon-on-insulator substrates are well known in the art, and convey certain advantages compared to standard silicon substrates. Several authors have demonstrated GaN-on-insulator substrates. Tauzin et al. [Electronics Letters 41, 668 (2005) transferred the topmost portion from a 4-μm-thick GaN-on-sapphire epilayer onto a second sapphire substrate by means of SmartCut™ layer-transfer technology. The crystalline quality of the transferred layer was not particularly high in this case. O. Moutanabbir and U. Gösele [J. Electronic Mater. 39, 482 (2010)] transferred a layer from a free-standing, pseudo-bulk GaN wafer of unspecified quality to sapphire. Sapphire, while readily available and convenient to work with, suffers from a relatively low thermal conductivity and has a significant mismatch in the coefficient of thermal expansion with respect to the GaN layer. In addition, in cases where the nitride crystal in a GaN-on-insulator wafer is spatially inhomogeneous, we are not aware of any teachings about the best way to arrange fabricated devices with respect to structures in the GaN layer.
What is needed is a more manufacturable solution for fabricating high-quality GaN-on-handle substrates or wafers that are optimized for down-stream device processing and device designs and processing methods that are optimized to take advantage of the properties of the wafer.